Hydrophilic-Like Sputtered AR Coating

ABSTRACT

An ophthalmic article having a coating system which provides antireflective and easy clean properties to the ophthalmic article. The coating system includes alternating layers of low refractive index metal oxide and high refractive index metal oxynitrides and corresponding high refractive index metal oxides. The coating system provides favorable surface energy to the ophthalmic article when at least one layer of the high refractive index metal oxynitride is encapsulated between two layers of low refractive index metal oxide.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 62/873,779 filed Jul. 12, 2019 entitled HYDROPHILIC-LIKE SPUTTEREDAR COATING, which is hereby incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is directed to optical coatings and, moreparticularly, to hydrophilic-like sputtered coatings that are easy toclean and anti-reflective.

BACKGROUND OF THE INVENTION

One or more functional coatings can be applied to a surface of anophthalmic article in order to impart different properties orcharacteristics to its surface. Such properties or characteristicsimparted by the coatings may include color, gloss, reflectivity,abrasion resistance, optical clarity, water repellency, resistance tofogging, anti-reflectivity, resistance to soiling, and ease of cleaning.Of these various properties, the surface properties or characteristicsof ease of cleaning and anti-reflectivity have potentially broadapplications in ophthalmic industries.

Dirt, oil, and dust are the major contaminants that build up anophthalmic lens. Depending on the wearer's environment, the type ofophthalmic lens coatings, and materials needed to clean them, theremoval of these contaminants is ongoing and often challenging.

In order to keep the surfaces of the ophthalmic lenses clean, manymanufacturers employ the use of hydrophobic coatings on these lenses andmarket the hydrophobic coatings as being more slippery or hydrophobic ontheir surface than competing eyewear and therefore is easier to clean.However, market surveys reveal that that these easy-cleaning coatingtechnologies using hydrophobic or slippery lens surfaces do not performat expected levels for several reasons.

The first reason is that a hydrophobic or slippery surface does notnecessarily mean that oil and dirt always fall off or are easy toremove. Instead, oil & dirt tend to be easier to move around on thesurface and in absence of friction from the surface, they tend to smearover the surface of the lens.

The second reason is that the current easy-cleaning coating technologiesusing hydrophobic surfaces are chiefly directed towards achieving thehighest possible contact angles for both water and oils. The reason forthese high contact angles is due to correlations between high contactangles for water and oil, and surface resistance to smudges,fingerprints, and ease of cleaning. Generally, a contact angle of thewater of >110° pre rub and >105° post rub is normally used. However, thehigh contact angle does not always indicate an easy to clean surfacesince the oils mixed with dirt tend to move or smear across the slipperylens surface.

The third reason is that the hydrophobic surface performance may not bemaintained over a long time. The hydrophobic coating deteriorates orabrades off overtime during the lens cleaning. When this happen, oilsand dirt build up on the lens and can be difficult to remove without theuse of soap or similar cleaning solutions.

Typically, these hydrophilic coatings rely on the photocatalyticactivity of the coating, the most common of this nature being a coatingof titania or titanium dioxide (TiO₂). As a wide band semiconductor,TiO₂ absorbs light in the UV wavelengths. The absorption processgenerates electron-hole pairs and the photo-generated holes are thecause of the hydrophilicity of the coating surface (water contact anglebelow) 10°. The trapping of contaminants like water or oils by the holeslead to the formation of charged species, for example, hydroxyl ions andhydroxyl radicals, by oxidation. These charged species can have severaleffects: a) they can generate hydrophilicity on the surface (throughsurface reorganization if TiO₂ increases the density of hydroxylradicals on the surface); b) they can provide a self-cleaning mechanismvia oxidation of surface contaminants; and c) catalytic effects forconversion of pollutants to nonhazardous materials.

The photocatalytic effect of a TiO₂ coating is the subject of manypatents including US2003/0048538 A1, U.S. Pat. Nos. 7,527,867,5,854,708, and 6,830,785, the contents of which are hereby incorporatedby reference. In these patents, the photocatalytic properties of TiO₂are used to provide increased hydrophilicity (water contact angle below10°) and in some cases a self-cleaning mechanism that helps to maintainthe hydrophilic properties when the surface becomes soiled.

In some cases, silicon dioxide (SiO₂) is either added into thephotocatalytic TiO₂ as a dopant, as seen in U.S. Pat. No. 6,830,785, oras a layer on top of TiO₂, as seen in US2003/0048538 A1, the contents ofwhich are hereby incorporated by reference, in order to enhance thehydrophilic behavior of the TiO₂ coating. The use of oxy-nitrides oftitanium (TiO_(x)N_(y)) as a photocatalyst is also discussed in thepublication by Asahi [“Visible Light Photo catalyst in Nitrogen DopedTitanium Oxides”, Asahi, Morikawa, Ohwaki, Aoki, Taga, Science 293 pg.269], the content of which is hereby incorporated by reference. Byadding nitrogen, the bandgap of the semiconductor is narrowed such thatabsorption of high energy visible light is able to generate electronhole pairs. The presence of photocatalytic behavior with TiOxNy issimilar to TiO₂ when exposed to UV irradiation. However, thephotocatalytic effects observed with TiO_(x)N_(y) (with either UV orvisible illumination) are substantially weaker than that of TiO₂ underUV illumination. In other words, TiO_(x)N_(y) as a photocatalyticmaterial is not as efficient as TiO₂ when converting photons into thedesired change in surface energy or reactivity.

However, these types of hydrophilic coatings are typically not durableover longer periods of time and cannot be used in applications whereabrasion is present. In addition, in these types of hydrophiliccoatings, the surface energy of the ophthalmic surface decreases overtime and eventually approaches zero, and therefore the hydrophiliccoatings no longer provide favorable surface energy to facilitate easycleaning property of the ophthalmic lens.

Hence, there exists a need to develop coatings and coating systems thatovercome the disadvantages of prior hydrophilic coatings by providingboth improved cleaning characteristics and improved durability overlonger periods of time.

SUMMARY OF THE INVENTION

The present invention provides coatings and coating systems that imparteffective easy-cleaning properties to a surface of an ophthalmicarticle. According to some embodiments, the coating system of theophthalmic article is achieved by providing a substrate having a surfaceand a plurality of alternating low refractive index layers comprising ametal oxide which includes silicon dioxide and high refractive indexlayers. The alternating high refractive index layers comprise a secondmetal oxide which includes titanium dioxide or zirconium dioxide, and atleast one metal oxynitride comprising titanium oxynitride or zirconiumoxynitride, all of which are deposited on the surface of the substrate.In this coating arrangement, the ophthalmic article comprises a surfacefree energy in a range of about 50-70 mN/m for a prolonged period forexample, nearly 40 days, when said at least one high refractive indextitanium oxynitride or zirconium oxynitride is encapsulated between twolayers of the silicon dioxide having low refractive index.

According to some embodiments of the present invention, a high indexMetal oxynitride (titanium or zirconium) is engineered into a modifiedanti-reflection optical stack to function as a hydrophilic type surfaceto increase its cleanability or an optical article. The layers arepreferably constructed within the antireflection (AR) optical stack sothat no other layers outside the AR stack are needed to make the opticalarticle easier to clean. Metal oxy-nitrides films, when used incombination and encapsulated between silicon dioxide generate thehydrophilic properties based on the nitrogen-to-oxygen ratio duringsputtering of the thin film AR.

In some embodiments of the present invention, a method of making anophthalmic article having easy-clean and anti-reflective properties isdescribed. The method comprises providing a substrate having a firstsurface and a plurality of alternating layers of low refractive indexmetal oxide and high refractive index metal oxide and metal oxynitrideare formed on the first surface. The plurality of alternating layersfurther comprises at least one high refractive index metal oxynitrideencapsulated between two layers of low refractive index metal oxide. Aneasy-cleaning property is imparted to the ophthalmic through theencapsulation of at least one high refractive index layer of metaloxynitride between the two layers of low refractive index metal oxide. Asurface cleanability ratio of the ophthalmic article in this coatingsystem is preferably greater than 90%.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features and advantages of which embodiments ofthe invention are capable of will be apparent and elucidated from thefollowing description of embodiments of the present invention, referencebeing made to the accompanying drawings, in which

FIG. 1 is a perspective view of a coated substrate according to oneembodiment of the present invention.

FIG. 2 is a perspective view of a coated substrate according to anotherembodiment of the present invention.

FIG. 3 is a table showing the differences among refractive index,thickness and surface roughness between zirconium oxide and zirconiumoxynitride.

FIG. 4 is a graph showing the combined plots of the measured contactangles (of water and diiodomethane) and the calculated surface energies(total, dispersive, and polar) on surfaces freshly coated with layers ofsilicon dioxide, freshly coated with layers of silicon dioxide andzirconium oxynitride and freshly coated with encapsulated zirconiumoxynitride between two silicon dioxide layers.

FIG. 5 is a graph showing the combined plots of the measured contactangles (of water and diiodomethane) and the calculated surface energies(total, dispersive, and polar) the surface coated with layers describedin FIG. 4 after 58 days of the experiment.

FIG. 6. is a comparative graph showing contact angles of water over timeon surfaces when coated with AR coatings containing SiO₂ and eithertitanium oxide or titanium oxynitride. The outer most layer is SiO₂ inthe stack design.

FIG. 7 is a comparative graph showing contact angles of water over timeon surfaces when coated with an AR stack containing SiO₂ and eitherzirconium oxide or zirconium oxynitride. The outer most layer is SiO₂ inthe stack design.

FIG. 8 is a comparative graph showing contact angles of diiodomethaneover time on surfaces when coated with and AR coating containing SiO₂and either titanium oxide or titanium oxynitride. The outer most layeris SiO₂ in the stack design.

FIG. 9 is a comparative graph showing contact angles of diiodomethaneover time on surfaces when coated with an AR coating with SiO₂ andeither zirconium oxide or zirconium oxynitride. The outer most layer isSiO₂ in the stack design.

FIG. 10 is a comparative graph showing surface free energies of thesurfaces over time when coated with an AR coating containing SiO₂ andeither titanium dioxide or titanium oxynitride. The outer most layer isSiO₂ in the stack design.

FIG. 11 is a comparative graph showing surface free energies of thesurfaces over time when coated with an AR coating containing SiO₂ andeither zirconium oxide or zirconium oxynitride. The outer most layer isSiO₂ in the stack design.

FIG. 12 is a comparative graph showing free energies of dispersivecomponents of the surfaces over time when coated with an AR coatingcontaining SiO₂ and either titanium dioxide or titanium oxynitride. Theouter most layer is SiO₂ in the stack design.

FIG. 13 is a comparative graph showing free energies of dispersivecomponents of the surfaces over time when coated with an AR coatingcontaining SiO₂ and either zirconium oxide or zirconium oxynitride. Theouter most layer is SiO₂ in the stack design.

FIG. 14 is a comparative graph showing free energies of polar componentsof the surfaces over time when coated with SiO₂ and either titaniumdioxide or titanium oxynitride. The outer most layer is SiO₂ in thestack design.

FIG. 15 is a comparative graph showing free energies of polar componentsof the surfaces over time when coated with SiO₂ and either zirconiumoxide or zirconium oxynitride. The outer most layer is SiO₂ in the stackdesign.

FIG. 16 is a comparative graph showing cleanability ratios betweenzirconium oxide or zirconium oxynitride used as the high refractiveindex layers in the antireflective and easy cleaning stack. The outermost layer is SiO₂ in the stack design.

FIG. 17 is a Table showing comparison of cleanability ratios amongcompetitors' hydrophobic coatings, the easier to clean coating inearlier U.S. patent Ser. No. 10/613,255B2, and the coatings disclosed inthe present invention (labeled “Hydrophil AR”).

DESCRIPTION OF EMBODIMENTS

Specific embodiments of the invention will now be described withreference to the accompanying drawings. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art. Theterminology used in the detailed description of the embodimentsillustrated in the accompanying drawings is not intended to be limitingof the invention. In the drawings, like numbers refer to like elements.

The present invention provides a coating system of an ophthalmic articlewhich comprises at least a coated layer of a high refractive index metaloxynitride. The presence of at least a layer of metal oxynitride into anantireflective optical stack of the ophthalmic article provides afavorable surface energy to render the surface hydrophilic in naturewhich enhances an easy clean property of the surface of the ophthalmicarticle from dirt, skin oil, and dust. The ophthalmic articles to whichthe easy-cleaning coating or layer of the present invention can beapplied include but are not limited to glass, plastics, metals, paintedor colored surfaces, and other materials where cleanability isdesirable.

In some embodiments of the present invention, an easy cleaning coatingor layer comprises at least a layer of high refractive index titaniumoxynitride or zirconium oxynitride which provides a surface of anophthalmic article with long lasting increased surface energy. In someembodiments, the easy clean and antireflective optical stack of theophthalmic article comprises at least a layer of a titanium oxynitrideor zirconium oxynitride along with layers of silicon dioxide. In someother embodiments, the easy clean and antireflective optical stack ofthe ophthalmic article comprises at least a layer of a titaniumoxynitride or zirconium oxynitride along with layers of silicon dioxideand titanium dioxide or zirconium dioxide.

In some embodiments of the present invention, a process to prepare anantireflective stack with easy clean property comprises using a DC pulsesputtering at 150 Khz in vacuum to deposit at least one layer of a highrefractive index titanium oxynitride or zirconium oxynitride into lowrefractive index layers of silicon dioxide. In some embodiments, thesurface of an easy clean and antireflective optical stack of theophthalmic article generates controlled hydrophilic surface energy whenat least a layer of a high refractive index titanium oxynitride orzirconium oxynitride is being encapsulated between two layers of lowrefractive index silicon dioxide in the optical stack.

According to some embodiments, a non-limiting example of a standardantireflective and easy clean stack design employs a five layerstructure of a L/H/L/H/L stack, where L is a low refractive indexsilicon dioxide layer, and H is a high refractive index layers oftitanium oxynitride, zirconium oxynitride, titanium dioxide or zirconiumdioxide. In some embodiments, the ophthalmic article generates longlasting and controlled hydrophilic surface energy when at least a highrefractive index layer comprises a titanium oxynitride or zirconiumoxynitride layer.

In some embodiments of the present invention, preparation of a titaniumoxynitride or zirconium oxynitride layer includes sputter depositionfrom a metal target of titanium or zirconium in presence of oxygen andnitrogen to form the desired metal oxynitride layer. In some embodimentsof the present invention, preparation of a low refractive index materialof silicon dioxide includes sputter deposition from a silicon target inpresence of oxygen to deposit silicon dioxide.

In some embodiments of the present invention, a standard vivid 5/7 CX/CC(CC-concave, CX-convex) and zirconium with 99.98% purity as the highrefractive index metal is used for sputtering. In some embodiments, asilicon with 99.999% purity as low refractive index material is used forsputtering. In some other embodiments, silicon is doped with 6% boron aslow refractive index material for all the controlled testing.

In some embodiments of the present invention, the sputtered gasescomprise argon, oxygen, and nitrogen at any given process flows.According to some embodiments, a mass flow controller used during theprocesses is 50 sccm for both argon and oxygen flows. When nitrogen isused as a sputtered gas, a 5 sccm mass flow controller is used insteadof a 50 sccm, because a small flow of 3.5 sccm is needed to coat thenitride. In some embodiments of the present invention, an adhesive layerof a silicon process is at about 20-30 angstroms during the testing.

In some embodiments, a method for making a metal oxynitride is performedby using a DC pulse Magnetron sputtering with metal mode using areactive plasma barrel. The sputtering system used in this invention isdetailed in the U.S. patent application 2014/074912, the content ofwhich is incorporated herein by reference. In the process of sputtering,the material is applied as a very thin metal and is rotated through areactive plasma. Due to the construction of the plasma source and thecathode placement, the majority of species of gas can be delivered atthe cathode or in the plasma barrel. In some embodiments, an inert gas,for example, argon, and a reactive gas, such as nitrogen, is deliveredat the cathode and another reactive gas, such as oxygen, is delivered atthe plasma barrel. In some embodiments, a 2.5 to 3.5 sccm mass flowcontroller is sufficient to get a metal oxynitride layer in a consistentprocess. In this invention, all samples are prepared using a Mycoat DCpulsed sputtering system with metal-mode plasma barrel for reaction ofthe metal film into oxides or oxynitrides.

In this invention, the anti-reflective color specification is used inthe test which is tracked from zero hours and over a period of time.Furthermore, in this invention, the hydrophilic antireflective processesare used with a number of different lens types. The non-limitingexamples of such lenses are Polycarbonate Tegra and Clear Blue Filter,CR39 with high refractive index of 1.67 and 1.70 respectively. Theoriginal antireflective recipe is modified for color and spectraadjustments as needed for specifications which had little effect on thesurface energy and cleanability results.

In some embodiments of the present invention, the high refractive indexlayers of titanium oxynitride or zirconium oxynitride work in threefolds in the antireflective stack of the ophthalmic article. A first wayis the change in surface morphology during the growth of a thin filmlayer of titanium oxynitride or zirconium oxynitride in the stack. Insome embodiments, a 10 nm thickness of a thin film layer of titaniumoxynitride or zirconium oxynitride work the same as a 100 nm thicknessof a thin film layer of titanium oxynitride or zirconium oxynitride inthe context of surface energy and/or surface morphology. In someembodiments, the placement of a thin film layer of titanium oxynitrideor zirconium oxynitride in the anti-reflective optical stack changes howthe overall optical stack behaves in terms of cleanability and surfacefree energy. According to some embodiments, a non-limiting example of astandard antireflective and easy clean stack design employs a five layerstructure of L/H/L/H/L stack, where L is a low index refractive indexsilicon dioxide layer, and H is a high refractive index layer of atleast a titanium oxynitride or zirconium oxynitride coating. In thisregard, high refractive index means an index of refraction that isapproximately greater than about 1.7 at a referenced wavelength, forexample a wavelength of about 550 nanometers. Low refractive index meansan index of refraction that is approximately less than about 1.5 at areferenced wavelength, for example a wavelength of about 550 nanometers.This type of columnar growth of a L/H/L/H/L stack also increases thesurface area and the increase in surface area plays a role in achievinga controlled surface free energy (SFE) which eventually leads to anincrease in easy clean property of the ophthalmic article. The columnargrowth may also result in an increased coefficient of friction on thesurface, resulting in a “grabby feel” to the lens surface.

A second way the presence of the metal (Ti/Zr) oxynitride layer/layersinfluence the antireflective stack is by providing a controlled surfacefree energy of the total optical antireflection stack. In someembodiments, the presence of the metal (Ti/Zr) oxynitride layer/layersinfluence the antireflective stack by providing a controlled surfaceenergy in a range of about 50-70 mn/m. In such embodiments, in which thecontrolled surface energy in a range of about 50-70 mn/m, each layer ofthe metal (Ti/Zr) oxynitride layer/layers interact with the otheroptical stack layers and contributes to the overall surface free energyof a hydrophilic surface and general cleanability of the surface.

A third way the presence of the metal (Ti/Zr) oxynitride layer/layersinfluence the hydrophilicity of the surface is by suspectedphotocatalytic properties of the titanium or zirconium oxynitride layerby photo-generating holes in presence of sunlight (photons) and therebycreating OH radicals by oxidizing surface water and oils by these holes.

Referring now to FIG. 1 of this invention, this figure shows anembodiment in which a surface of an article 10 (e.g., an optical lens)is provided with a durable anti-reflective coating with easy-cleaningproperties. According to this embodiment of FIG. 1, a coating system 20comprising a five layer stack of alternating L/H/L/H/L layers, where Lis a low refractive index silicon dioxide layer (20 a, 20 c, 20 e) and His a high refractive index layer (20 b or 20 d), at least one of whichis composed of titanium oxynitride or zirconium oxynitride (20 b or 20d). The other high refractive index layer(s) may be a titanium dioxide,zirconium dioxide, titanium oxynitride, or zirconium oxynitride layer.The pre-tuned anti-reflective and easy clean stack 20 may employ, forexample, at least three layers alternating between high and low indexrefractive layers, but may also not necessarily be limited in the numberof alternating layers (e.g., the stack 20 may include 3, 4, 5, 6, 7, 8,9, 10, 11, 12, 13, 14, 15, 16, or greater numbers of layers). In thisrespect, the stack may have layers 20 n where n equals the number oflayers present.

For example, the refractive layers 20 n may comprise alternating layersof low refractive index silicon dioxide and high refractive indextitanium oxynitride. In another example, the refractive layers 20 n maycomprise alternating layers of low refractive index silicon dioxideand 1) one or more layers of high refractive index titanium oxynitride,and 2) one or more layers of high refractive index high refractive indextitanium dioxide. In another example, the refractive layers 20 n maycomprise alternating layers of low refractive index silicon dioxide andhigh refractive index zirconium oxynitride. In another example, therefractive layers 20 n may comprise alternating layers of low refractiveindex silicon dioxide and 1) one or more layers of high refractive indexzirconium oxynitride and 2) one or more layers of high refractive indexzirconium dioxide. In all the embodiments of the present invention, theeasy clean and antireflective optical stack of the ophthalmic articlecomprises at least a layer of a high refractive index titaniumoxynitride or zirconium oxynitride along with layers of low refractiveindex silicon dioxide and high refractive index layers of titaniumdioxide or zirconium dioxide. In some embodiments, at least a layer of ahigh refractive index titanium oxynitride or zirconium oxynitride (FIG.1, 20 b or 20 d) is encapsulated between two layers of low refractiveindex silicon dioxide (20 a, 20 c, 20 e) within the stack.

FIG. 2 shows an alternative example of an embodiment of the invention inwhich a coating system 20 comprises a seven layer stack of alternatingL/H/L/H/L/H/L layers, where L is a low index refractive index silicondioxide layer (20 a, 20 c, 20 e, 20 g) and H is a high refractive indexlayer, wherein at least one of the high refractive index layers is atitanium oxynitride or zirconium oxynitride (20 b or 20 d or 20 f)coating/layer. The other high refractive index layers may be titaniumdioxide or zirconium dioxide layers. The pre-tuned anti-reflective andeasy clean stack 20 may employ, for example, at least three layersalternating between high and low index refractive layers, but may alsonot necessarily be limited in the number of alternating layers (e.g.,the stack 20 may include 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,16, or greater numbers of layers). In this respect, the stack may havelayers 20 n where n equals the number of layers present.

Referring now to the table of FIG. 3, this table compares the differenceof refractive index, thickness, and surface roughness between highrefractive index layers of zirconium oxynitride and zirconium oxide andan ellipsometer is used to measure this data. The thin films ofzirconium oxynitride and zirconium dioxide are coated and measured onfused silica. The silica is normalized out of the measurement. The datashows very little difference in the index of refraction (e.g., adifference of 0.0032) and optical composition of the materials betweenlayers of zirconium oxynitride and zirconium dioxide but column 3 in thetable shows that there is a surface roughness difference betweenzirconium oxynitride and zirconium dioxide (e.g., a difference of about0.63 nm). The high refractive index coating of zirconium oxynitride hasa surface roughness of 4.43 nm, which higher than the surface roughnessof 3.80 nm of the high refractive index zirconium dioxide coating. Sinceincreased surface roughness typically correlates with a more hydrophilicsurface, the high refractive index coating of zirconium oxynitride witha higher surface roughness of 4.43 nm tends to be more hydrophilic innature compared to the high refractive index coating of zirconiumdioxide with a surface roughness of 3.80 nm.

FIG. 4 illustrates a graphical representation of both the measuredcontact angles (in water and diiodomethane) and the calculated surfacefree energies (total, dispersive, and polar) of the layers of silicondioxide, layers of silicon dioxide with zirconium oxynitride, and alayer of zirconium oxynitride encapsulated between layers of silicondioxide. Note, the date 8/1/18 refers to the sample creation date (i.e.zero hour measurement). In FIG. 4, an anti-reflective, easy clean stackfrom single layers of high refractive index and low refractive indexmaterials of different thickness are assembled and the contact angles(in water and diiodomethane) and the total surface free energies (total,dispersive, and polar) are measured with a goniometer. The experimentshows that the change in contact angles and the total surface freeenergies depend upon the layers and the sequences of the individuallayers. Herein, the total surface free energy is made up of thedispersive and polar energy components. Atoms and molecules which causesthe surface energy/tension of a substance can be explained by differenttypes of interactions among atoms and molecules on the surfaces. Forexample, interactions caused by temporary fluctuations of the chargedistribution in the atoms/molecules are called dispersive interactions(for example, van der Waals interaction) and contributes as thedispersive free energy towards the total surface free energy. However,the polar interactions comprise Coulomb interactions between permanentdipoles and between permanent and induced dipoles (for example, hydrogenbonds) and contributes as the polar free energy towards the totalsurface free energy. Therefore, the surface energy/tension of componentsis additively made up of dispersive and polar energy of the surfaces.FIG. 5 refers to a graphical representation of both the measured contactangles (in water and diiodomethane) and the calculated surface freeenergies (total, dispersive, and polar) of the surfaces of silicondioxide, layers of silicon dioxide with zirconium oxynitride, and alayer of zirconium oxynitride encapsulated between layers of silicondioxide. Note, the date 9/27/18 refers the measurement date after 58days of the sample creation date of Aug. 1, 2018 shown in FIG. 4. FIG. 5shows that the measured contact angles of the layer of zirconiumoxynitride grown on a single silicon dioxide layer is higher than thelayer of zirconium oxynitride encapsulated between layers of silicondioxide in water and diiodomethane. Whereas, the calculated surface freeenergy and the polar free energy of the layer of zirconium oxynitrideencapsulated between layers of silicon dioxide is higher than whensingle layer of zirconium oxynitride is grown on silicon dioxide alone(i.e., non-encapsulated) after 58 days of the start of the experiment.It may be noted from FIG. 5 that the dispersive free energies do notchange much over time between zirconium oxynitride encapsulated betweenlayers of silicon dioxide and single layer of zirconium oxynitride grownon silicon dioxide alone (i.e., non-encapsulated). The encapsulation ofthe layer of high refractive index zirconium oxynitride between layersof low refractive index silicon dioxide has a significant effect on thepolar component of the surface free energy which has been shown in thelater part of this invention.

FIGS. 6 and 7 of this invention show a comparison of the measuredcontact angles of deionized water over a period of time between highrefractive index layers of titanium dioxide and titanium oxynitride(FIG. 6) and high refractive index layers of zirconium dioxide andzirconium oxynitride (FIG. 7). In this comparative experiment, a normalvivid alternating 5/7 layer stack with the high index layers ofzirconium dioxide and low index layers of silicon dioxide is used as thebaseline. FIG. 6 shows that the measured contact angles of deionizedwater for the stack of titanium dioxide layers are much higher than themeasured contact angles of deionized water for the stack of titaniumoxynitride layers after 10 days, 20 days and more than 35 days of thestart of the experiment. Similarly, FIG. 7 shows that the measuredcontact angles of deionized water for the stack of zirconium dioxidelayers are much higher than the measured contact angles of deionizedwater for the stack of zirconium oxynitride layers after 5 days and 10days of the start of the experiment.

Referring to FIGS. 8 and 9 of this invention, these figures showcomparison of the measured contact angles of diiodomethane over a periodof time between high refractive index layers of titanium dioxide andtitanium oxynitride (FIG. 8) and high refractive index layers ofzirconium dioxide and zirconium oxynitride (FIG. 9). In this comparativeexperiment, a normal vivid 5/7 layers stack with the high index layersof zirconium dioxide and low index layers of silicon dioxide is used asthe baseline. FIG. 8 shows that the measured contact angles ofdiiodomethane for the stack of titanium dioxide layers are much higherthan the measured contact angles of diiodomethane for the stack oftitanium oxynitride layers after 10 days and 20 days and 30 days of thestart of the experiment. Similarly, FIG. 9 shows that the measuredcontact angles of diiodomethane for the stack of zirconium dioxidelayers are much higher than the measured contact angles of diiodomethanefor the stack of zirconium oxynitride layers after 5 days and 10 days ofthe start of the experiment.

The measurements of the contact angles shown in FIGS. 6-9 are then usedto determine the total surface free energy (SFE) and the dispersive andpolar components surface energy of the surfaces in the experiments shownin the following FIGS. 10-15.

FIGS. 10 and 11 of this invention show comparative experiments of themeasured total surface free energy (SFE) over a period of time between astack including high refractive index layers of titanium dioxide andtitanium oxynitride (FIG. 10) and a stack including high refractiveindex layers of zirconium dioxide and zirconium oxynitride (FIG. 11).FIG. 10 shows that the measured total surface free energy (SFE) for thestack of titanium oxynitride layers are much higher than the measuredtotal surface free energy (SFE) for the stack of titanium dioxide layersafter 5 days, 10 days, 20 days and nearly 40 days of the start of theexperiment. Similarly, FIG. 11 shows that the measured total surfacefree energy (SFE) for the stack of zirconium oxynitride layers are muchhigher than the measured total surface free energy (SFE) for the stackof titanium dioxide layers after 5 days and 10 days of the start of theexperiment. In some embodiments, the resulting total surface energy ofthe metal (Ti/Zr) oxynitrides based antireflective structures is betweenabout 50-70 mN/m.

FIGS. 12 and 13 of this invention show comparative experiments of themeasured dispersive components surface energy over a period of timebetween at stack including high refractive index layers of titaniumdioxide and titanium oxynitride (FIG. 12) and a stack including highrefractive index layers of zirconium dioxide and zirconium oxynitride(FIG. 13). FIG. 12 shows that the measured dispersive components surfaceenergies between layers of titanium dioxide and titanium oxynitridecoalesce to about 40 mN/m after nearly 40 days of the start of theexperiment. Similarly, FIG. 13 shows that the measured dispersivecomponents surface energies between layers of zirconium dioxide andzirconium oxynitride do not differentiate much after 5 days and 10 daysof the start of the experiment. These experiments shown in FIGS. 12 and13 illustrate that the dispersive component of surface energy has littleeffect or variation between the stacks made of the layers of titaniumdioxide and titanium oxynitride or the stacks made of the layers ofzirconium dioxide and zirconium oxynitride over time. From thisexperiment, it may be concluded that the dispersive interactions (forexample, van der Waals interactions) among atoms and molecules caused bytemporary fluctuations of the charge distribution have very littledifference between layers of metal oxide and metal oxynitrides where themetals are taken from at least, but not limited to titanium andzirconium.

FIGS. 14 and 15 of this invention show comparative experiments of themeasured polar components surface energy over a period of time betweenhigh refractive index layers of titanium dioxide and titanium oxynitride(FIG. 14) and high refractive index layers of zirconium dioxide andzirconium oxynitride (FIG. 15). FIG. 14 shows that the measured polarcomponents surface energies of titanium oxynitride is much higher thanthe measured polar components surface energies of titanium dioxide after5 days, 10 days, 20 days and nearly 40 days of the start of theexperiment. Similarly, FIG. 15 shows that the measured polar componentssurface energies of zirconium oxynitride is much higher than themeasured polar components surface energies of zirconium dioxide after 5days and 10 days of the start of the experiment. From this experiment,it may be concluded that the polar interactions (for example, hydrogenbonds) between permanent dipoles and between permanent and induceddipoles is much higher for a layer of zirconium oxynitride than a layerof zirconium dioxide.

The graphs in FIGS. 14 and 15 show that with the coatings using only thehigh index metal (Ti/Zr) oxides, the polar energy decreases over timeapproaching to zero, which tends to result in decreased hydrophiliccharacteristics. In contrast, the metal (Ti/Zr) oxynitrides show aninitial reduction in the polar surface energy and then the polar surfaceenergy stabilizes at a much higher non-zero value, which helps maintainmore stable hydrophilic characteristics. In some embodiments, the polarenergy of the metal (Ti/Zr) oxynitrides is between about 15-40 mN/m.According to some embodiments of this invention, the stability of thepolar component energy of the metal (Ti/Zr) oxynitrides may be dependenton the optimum amount of nitrogen used in the preparation of the metal(Ti/Zr) oxynitride thin film. If more than this amount of nitrogen isused in the sputtering process, the hydrophilic characteristic of themetal (Ti/Zr) oxynitride films may not be stable and the controlledtotal surface energy of the metal (Ti/Zr) oxynitride films of about50-70 mN/m range may not be obtained.

It should be noted that the presence of a SiO₂ layer alone in theoptical stack will render a hydrophilic like property to theanti-reflection optical stack for a short period of time and then thishydrophilic property will diminish over time. Description of FIGS. 6-15above shows that the presence of high refractive index metal-oxynitridecoatings embedded between SiO₂ layers create permanancy to thehydrophilic like behavior of the anti-reflection optical stacks. Whenthe high refractive index metal-oxynitride encapsulated in between SiO₂layers, the combined layers work synergistically together. In all theabove described anti-reflection optical stacks in FIGS. 6-15, the toplayer always remains SiO₂. The surface energy data from FIGS. 10-15shows that the use of the oxynitride coating leads to an increase in thesurface energy for the entire anti-reflection optical stack.

Referring now to FIG. 16 of this invention, this figure shows acleanability test which is employed to determine the ease of removingoily residue from a lens surface. At the beginning of this experiment, asynthetic skin oil (sebum) is applied using a tampo rubber stamper. Theuse of the tampo stamper is needed to apply a controlled amount sebumgiving a predictable amount of optical haze. The sebum temperature iscontrolled at 60° C. Lenses with either a base curve of 4 or 6 diopterswere used. Limiting the curve range improves repeatability of the test.The optical haze of the sample was then measured three times afterturning the lens 120 degrees. The average of these measurements is thereported initial haze. The sample is placed in a rub testing system with2.2 kg weight on top of a soft form pad with a polyester cloth with theweave running across the sample in 90° angle to the stroke. After sixstrokes the cloth is changed, and haze was measured. At the end of 18strokes, the finial haze measurement is taken. In some embodiments ofthe invention, the stamping of the sebum should be ˜35% transmissionusing the haze guard. This is because some of the surfaces having somedifferent textures. Heating the sebum and stamping pressure aids in theuniformity and reproducibly of the haze starting point. As stated abovethe sample is rotated ˜120 degrees on each haze measurement and theaverage is taken. In hydrophobic samples, measurements of the hazesometimes get worst due to the smearing of the sebum. This is one of themajor drawbacks of the hydrophobic coating in which oil and dirt tend tomove around on the surface because of the low surface energy.

From the haze readings after initial stamping and after 18 strokes witha polyester cloth, a cleanability ratio may be calculated by subtracting18 strokes finial haze reading from the initial stamp haze reading, anddividing the result by initial stamp haze reading and multiplying by100, which is represented here by the mathematical equation of“Cleanability Ratio”=(Initial reading-final reading)/initialreading*100.

The above equation is used to compare the “Cleanability Ratios” ofdifferent materials, lenses of different manufactures and manufacturingprocesses. FIG. 16 shows a comparison of the “Cleanability Ratios” ofzirconium oxynitride vs the zirconium dioxide used as the high indexlayers of the anti-reflective structures. FIG. 16 further shows that theinitial haze reading of the stack of anti-reflective structure preparedusing zirconium oxide as the high refractive index layer being 33.88 andthe initial haze reading of the stack of anti-reflective structureprepared using zirconium oxynitride as the high refractive index layerbeing 37.88. After 18 strokes with a polyester cloth, the haze readingof the stack of anti-reflective structure prepared using zirconium oxideas the high refractive index layer being 23.58 and the haze reading ofthe stack of anti-reflective structure prepared using zirconiumoxynitride as the high refractive index layer being 0.87. The“Cleanability Ratios” were calculated using the above equation and FIG.16 shows that the “Cleanability Ratio” of the stack of anti-reflectivestructure prepared by using high index zirconium oxynitride layers ismuch higher (97.63) than the “Cleanability Ratio” of the stack ofanti-reflective structure prepared by using high index zirconium dioxidelayers.

FIG. 17 shows comparison of cleanability ratios among competitors'hydrophobic coatings, easier-to-clean coating in Applicant's earlierapplication U.S. Pub. No. 2015/0226886, the content of which isincorporated herein by reference, and the coatings disclosed in thepresent invention (labeled Hydrophil AR). It may be concluded from FIG.17 that both the easier to clean coatings in Applicant's earlierapplication U.S. Pub. No. 2015/0226886 and the easier-to-clean coatingof the present invention (labeled Hydrophil AR) provide surfaces whichare more effectively cleaned by wiping than the industry standardhydrophobic coatings shown in comparative examples of 1-6 in FIG. 17.For example, the cleanability ratios of the industry standardhydrophobic coatings, shown in comparative examples of 1-6, are in theranges between 17%-70%. Whereas the cleanability ratios of theApplicant's application U.S. Pub. No. 2015/0226886 and the presentinvention are 92% and 95%, respectively. Hence, the lens according tothe present invention shows greater cleanability than the currentlymarketed “easy-cleaning” lenses tested.

Although the invention has been described in terms of particularembodiments and applications, one of ordinary skill in the art, in lightof this teaching, can generate additional embodiments and modificationswithout departing from the spirit of or exceeding the scope of theclaimed invention. Accordingly, it is to be understood that the drawingsand descriptions herein are proffered by way of example to facilitatecomprehension of the invention and should not be construed to limit thescope thereof.

1. An ophthalmic article having easy-clean and anti-reflectiveproperties comprising: a substrate having a surface; and, a stack onsaid surface; said stack comprising a plurality of alternating lowrefractive index layers comprising a metal oxide and high refractiveindex layers comprising 1) at least one metal oxynitride layer, or 2) atleast one metal oxynitride layer and at least one metal oxide layer. 2.The ophthalmic article of claim 1, wherein said ophthalmic articlecomprises a surface free energy in a range of about 50-70 mN/m for aprolonged period when said at least one high refractive index metaloxynitride layer is encapsulated between two layers of said lowrefractive index metal oxide.
 3. The ophthalmic article of claim 1,wherein said low refractive index metal oxide comprises silicon dioxide.4. The ophthalmic article of claim 1, wherein said high refractive indexmetal oxide comprises titanium dioxide or zirconium dioxide.
 5. Theophthalmic article of claim 1, wherein said at least one high refractiveindex metal oxynitride comprises titanium oxynitride or zirconiumoxynitride.
 6. The ophthalmic article of claim 1, wherein saidophthalmic article comprises a polar surface energy in a range of about15-40 mN/m for a prolonged period when said at least one high refractiveindex metal oxynitride is encapsulated between said two layers of saidlow refractive index metal oxide.
 7. The ophthalmic article of claim 6,wherein said at least one high refractive index metal oxynitridecomprises zirconium oxynitride which is encapsulated between said twolayers of said low refractive index silicon dioxide.
 8. The ophthalmicarticle of claim 6, wherein said at least one high refractive indexmetal oxynitride comprises titanium oxynitride which is encapsulatedbetween said two layers of said low refractive index silicon dioxide. 9.The ophthalmic article of claim 1, wherein a surface cleanability ratioof the ophthalmic article, when said at least one high refractive indexmetal oxynitride is encapsulated between two layers of said lowrefractive index metal oxide, is greater than 90%.
 10. The ophthalmicarticle of claim 9, wherein said surface cleanability ratio of theophthalmic article is 97.63% when said at least one high refractiveindex metal oxynitride comprising zirconium oxynitride is encapsulatedbetween two layers of said low refractive index metal oxide comprisingsilicon dioxide.
 11. An optical stack that imparts easy-cleaning andanti-reflective properties on a surface comprising: at least one highrefractive index layer of a metal oxynitride encapsulated between twolow refractive index layers of metal oxide.
 12. The optical stack ofclaim 11, wherein said high refractive index layer of said metaloxynitride comprises titanium oxynitride or zirconium oxynitride. 13.The optical stack of claim 11, wherein said low refractive index layersof said metal oxide comprises silicon dioxide.
 14. The optical stack ofclaim 11, wherein said high refractive index layer of said metal oxidecorresponding to said metal oxynitride comprises titanium dioxide orzirconium dioxide.
 15. The optical stack of claim 11, wherein a surfacefree energy of said optical stack, comprising high refractive indexlayer of said metal oxynitride encapsulated between said two lowrefractive index layers of metal oxide, remains in a range of about50-70 mN/m for about 40 days of time.
 16. The optical stack of claim 11,wherein said optical stack comprises a polar surface energy in a rangeof about 15-40 mN/m for about 40 days of time when said at least onehigh refractive index metal oxynitride is encapsulated between said twolow refractive index layers of metal oxide.
 17. The optical stack ofclaim 11, wherein said high refractive index layer of said metaloxynitride and said high refractive index layer of said metal oxidecorresponding to said metal oxynitride have about same refractiveindexes.
 18. The optical stack of claim 11, wherein said high refractiveindex layer of said metal oxynitride having a surface roughness higherthan a surface roughness of said high refractive index layer of saidmetal oxide corresponding to said metal oxynitride.
 19. A method ofmaking an ophthalmic article having easy-clean and anti-reflectiveproperties comprising: providing a substrate having a surface; and,forming a stack on said surface; said stack comprising a plurality ofalternating layers of low refractive index metal oxide and highrefractive index layers comprising 1) at least one metal oxynitridelayer, or 2) at least one metal oxynitride layer and at least one metaloxide layer; wherein a surface cleanability ratio of said ophthalmicarticle being greater than 90%.
 20. The method of claim 19, wherein saidmethod further comprises imparting said ophthalmic article with saideasy clean property through an encapsulation of said at least one highrefractive index layer of metal oxynitride between two layers of lowrefractive index metal oxide.
 21. The method of claim 19, wherein saidstep of forming said plurality of alternating layers of low refractiveindex metal oxide and high refractive index metal oxide and said atleast a layer of high refractive index metal oxynitride on said surfacecomprises coating said surface with alternating layers of low refractiveindex silicon dioxide and high refractive index titanium dioxide orzirconium dioxide and high refractive index titanium oxynitride orzirconium oxynitride.
 22. The method of claim 20, wherein said step ofimparting said ophthalmic article with said easy-clean property throughsaid encapsulation of said at least one high refractive index layer ofmetal oxynitride between two layers of said low refractive index metaloxide comprises encapsulating said high refractive index layer oftitanium oxynitride or zirconium oxynitride between two layers of lowrefractive index silicon dioxide.